Introduction
PREAMBLE
Students are required to work individually to construct a model of truss
structure and design an experiment procedure to investigate its loaddeflection behaviour. The proposed truss structure should be able to
carry as much load as possible. As engineer, the responsibility is not only
to design a safe truss structure to carry required loads, but also to make
sure that it is cost effective. To simulate this process, the strength to
weight ratio can be calculated by dividing the maximum load carried by
the weight of the truss.
Objective
To conduct the truss structure experiment, propose suitable
procedure, analyse and interpreted data collected.
Learning Outcomes
At the end of this practical project, student should be able to:
1. Identify problems for investigation of truss structure
2. Propose procedure for construction and experiment
3. Analyse and interpreted data from the truss experiment
Theoretical Background
Trusses are the key engineering feature in the emerging civil engineering
contest. Indeed, long span structures with light weight is the main
reason for the increase in the demand of trusses in the construction
industry. Since from the usage of steel as a construction material, due to
its higher strength with lower mass, trusses took a major role in the civil
structures together with the advancement of steel industry. Over the
past years and even for now considering aesthetic feature these trusses
are made with the timber planks as well. Roof trusses, bridges, electricity
and telecom towers and even the structural frames are making use of
these trusses as their integral structural forms.
Trusses are simply defined as triangulation of members to make the
stabilized structure. Triangulation is the stable configuration
mathematically. Generally, a truss has the members called as top chord,
bottom chord, vertical chord and diagonal chord. The main functions of
the trusses are carrying the loads from the over structures and providing
adequate lateral stability to the entire structure.
There are some basic assumptions in the designing process. It should be
clarified that the construction of the trusses should conform with the
design assumptions to avoid the unwanted failures due to the dispersion
of the forces and loads. Several assumptions in truss design are such as
truss members will carry only the axial forces. The nodes i.e the
connections of the members are designed as pinned joints so that
moments won’t be transferred to the members of the truss. All the
external loads and the reactions are act only on the nodes. Generally,
the truss should be in a plane. Typically the members of the trusses are
made as I sections, angles, T sections, Tube sections, Square sections and
channel sections. I sections are more preferable as a optimized section
in terms of the structural forces.
PROBLEM STATEMENT
Truss, in engineering, a structural member usually fabricated from
straight pieces of metal or timber to form a series of triangles lying in a
single plane. (A triangle cannot be distorted by stress.) A truss gives a
stable form capable of supporting considerable external load over a
large span with the component parts stressed primarily in axial tension
or compression. The individual pieces intersect at truss joints, or panel
points. The connected pieces forming the top and bottom of the truss
are referred to respectively as the top and bottom chords. The sloping
and vertical pieces connecting the chords are collectively referred to as
the web of the truss. Thus, this experiment is conducted to show an
example of the trusses in a build structure and how to find the
maximum load that it can carried before collapsed.
WAYS AND MEANS
Apparatus
1.
2.
3.
4.
5.
6.
7.
Straw
Ice cream stick
Sole tap
Scales
Book
Ruler
Strong glue
Procedure
1. A truss structure (bridge model) is constructed by using ice
cream stick and sole tap, and strong glue
2. The length of the structure is measures and lengthwise 30 cm.
3. The height of the structure is measured and as tall as 10 cm
4. 3 different book and the model structure is weighed.
5. The jointed trusses is checked before starting the putting the
books on the structure.
6. The books is carefully put on the structure one by one
(gradually increased) at the centre of the structure until the
structure collapsed.
7. The data is recorded
RESULT
Calculation
Weight of the bridge model, B = 300g
Weight of the Book 1 = 500g
Weight of the Book 1 = 600g
Weight of the Book 1 = 400g
Test Load
1
2
3
Book 1
Book 2 + Book 1
Book 3 + Book 2 + Book 1
Weight of
Load, L (g)
500
1100
1500
Ratio (L/B)
(g)
1.67
3.66
5.00
..
Discussion
In this experiment , there are three different book that have different
weigh used as the load. The truss structure which is bridge model is
constructed by using ice cream stick and the trusses are attached
together by using sole tape and strong glue which is to make sure the
strung can hold the load efficiently. Before starting the test, the model
structure is weighed individually so the load that can be carried easily
known. After the third book is put on the model, the model immediately
collapsed and shows that the structure only able to carry 3 books only
which the total weight of the model structure. In the first hypothesis,
the model should be able to accommodate more than 3 books but it cant
which show there might be slightly error in the experiment. It can be
that the glue used to attach the altogether might be not strong enough
to accommodate the load. To overcome this, make sure to check the
apparatus used before starting the experiment .
Conclusion
In conclusion, a truss is a structure composed of members connected
together to form a rigid framework. Like in this structure, the members
are the load-carrying components which are. In most trusses, members
are arranged in interconnected tri-angles, as shown below. Because of
this configuration, truss members carry load primarily in tension and
compression. In this model structure the model able to accommodate
with the load because trusses are very strong for their weight, they are
often used to span long distances. They have been used extensively in
bridges since the early 19th century; however, truss bridges have
become somewhat less common in recent years. Today trusses are often
used in the roofs of buildings and stadiums, in towers, construction
cranes, and many similar structures and machines. Trusses, like all
structures, are designed by civil engineers with special expertise in
structural analysis and design. These men and women are called
structural engineers. With that stated, the objective of this experiment
is achieved.
References
1. https://basiccivilengineering.com/2019/06/trusses-types-trusses.html
2. https://allinonehomeschool.files.wordpress.com/2018/03/learning_activity_1.pdf